Material and method for lubricating the metal surfaces of an earth-pressure tunnel boring machine

ABSTRACT

A method of boring a tunnel with a tunnel boring machine comprising injecting into the formation to be bored just before the cutting tools of the boring machine and optionally into the internal discharge chamber of the boring machine, an aqueous foam containing at least one clay, at least one surfactant and at least one gas in proportion to produce a good quality, stable foam with the formation material and discharging the material from the tunnel via the discharge of the boring machine.

The present invention concerns the technical field of machines used tobore tunnels, commonly called “tunnel boring machines.”

It is known that these machines are capable of boring into subterraneanformations, a tunnel whose diameter corresponds directly to the finaldiameter of the work to be performed, or essentially so. It naturallyinvolves extremely powerful and complex machines whose operatingconstraints and requirements are in proportion to their design.

Among the constraints, we shall consider here in particular the problemsassociated with the attack of the underground formation by the boringtools. This naturally causes substantial wear on these tools, and it isunderstood that this is related to the hardness of the rock. Anotherrelated problem resides in the evacuation of the cuttings and thedebris.

There is also a substantial wearing of the components used forevacuation of the debris, especially if it involves an endless screw orArchimedes screw, either on the screw or on its metal envelope, andoften also on the tunnel machine skirt.

It will be recalled that there are two main types of tunnel boringmachines: “bedrock” tunnel boring machines designed to attack terrainswith a good deal of rock and the like, and “confinement” tunnel boringmachines designed to operate on soil of ordinary content (alluvial soil,sand, clays) or wetlands.

By the nature of the soil tunneled, the latter boring machines are lessseverely confronted with wear problems. On the other hand, they canoperate in an easily worked or liquid (water bearing) environment, andthey contain a system which ensures imperviousness behind the boringmachine head.

The acuteness of the wear problems will also be recalled. The boringmachines are actually machines whose wearing parts are by definitionvery hard to access, whether it involves the screw, the tools andcutting wheels for boring, the front surface of the tunnel boringmachine, or its lateral skirt. Moreover, when a wearing phenomenon makesit necessary to replace a part, it is necessary to stop the machine, andsometimes to move it back and partially dismantle it. These downtimestranslate into enormous financial losses and any gain in matters ofprolonging the service life of a part is immediately and very keenlyfelt.

prior art discloses injecting water or a watery fluid into the head ofthe tunnel boring machine. By known appropriate devices, this fluid isbrought to the cutting tools and at this level is brought into contactwith the formation to be bored.

This fluid fulfills a most classical dual function, which is tolubricate the contact zone between the cutting tool and the rock, on theone hand, and on the other hand to permit an easier evacuation of thecuttings in the form of a slurry loaded with debris, and to reduce theformation of dust.

However, this is only a palliative measure and the industry in questionfor many years has been confronted more frequently with increasinglymore acute problems connected with the performance of the machines andthe requirements of the users.

Foams have likewise been used comprised only of water and surface-activeagent(s) (and a gas such as air) in the case of confinement boringmachines. The purpose of the water foam is this case to fluidize theexcavated material, to improve the permeability of the soil (which ispossible precisely by virtue of the nature of the terrain encountered bythis type of boring machine) and thus to reduce the torque applied tothe machine.

This technique has been tried in rock tunneling machines and isineffective, i.e., it does not provide substantial progress.

The use of lubricating systems has likewise been tried, also withoutsignificant results.

According to the invention, the problems described above are improved toa surprising degree.

According to the invention, into the head of the tunnel boring machine,not a water fluid or a water foam or lubricant, but a watery foamcomposition heavily loaded with clay(s) is injected.

This composition is injected in the form of a foam formed eitherupstream of the head of the boring machine, or in situ.

This results in an altogether unexpected reduction in wear as well assignificantly easier extraction of the cuttings.

The clay foam composition also makes it possible to reduce greatly thevolume of water necessary, which bears on the enormous volumes and thushas great impact on respecting the environment and, moreover, theprocessing of the excavated material in view of respecting theenvironment is easier, some excavated material not even needing to betreated.

Without wanting to be limited by any theory, it has been noted that thereduction of wear seems to derive essentially from the occurrence ofcoating of the rock fragments by a layer of composition according to theinvention.

Thus, wear is reduced not only by lubrication or fluidization of thesurrounding medium, but essentially by a new function which reduces theabrasive nature of the rock itself providing a radical solution to thewear problems.

Other features and advantages of the invention will be better understoodupon reading the description following and referring to the encloseddrawing, in which:

FIG. 1 represents schematically and in transverse cross section a tunnelboring machine in operation.

FIG. 2 represents specific details of the boring machine according toFIG. 1.

FIG. 3 represents schematically the jacks and concrete “tubes” systemused simultaneously to advance the boring machine and shore up the wallof the tunnel behind the machine.

FIG. 4 represents the test cell developed to evaluate the effectivenessof the invention compared to prior art.

In this design identical reference symbols have identical meaning asfollows:

1. underground formation.

2. rotary head of boring machine.

3. boring machine chamber.

4, 5. excavated material extraction system: 5 endless screw, 4 tunnel(or casing) of the screw).

6. excavated material.

7. front face of the boring machine head.

8. boring machine skirt.

9. body (fixed) of the boring machine.

10. general circulation of the excavated material.

11. cutting space.

12. overcut space.

13. skirt—wall interspace.

14. excavated material fragment.

15. back face of the head.

20. cutting wheel and its support.

21. overcut wheel and its support.

22. injection point in the front face.

23. injection point in the back face.

24. overcut wheel.

25. cutting wheel.

30. tube (of concrete).

31. formation—tube contact wall.

32. thrust jack.

40. receptacle.

41. wear plate.

42. test material.

43. shaft.

As will be recalled briefly here, a tunnel boring machine designed tobore a tunnel in a formation (1) comprises essentially a cylindricalbody (9) including the appropriate machinery, and a head (2) mountedpivoting on the front of the body. This head carries the cutting toolswhich are comprised of cutting wheels (25) and supports (20) and whereapplicable, “overcut” cutting wheels (24) and supports.

The cutting tools (and where applicable those of overcut) attack theformation (1) by their own rotation associated with the rotation of thehead (2). Within the scope of the classical method fluid, generallywatery, is injected into the cutting space (11) and into the insidechamber (3) as well as where applicable into the overcut space (12) tolimit the wear on the parts and facilitate the extraction of theexcavated material toward the rear of the boring machine.

This extraction is classically done by systems inside the body of theboring machine, generally a belt or endless screw. By way of anon-limiting [example], there is represented in FIG. 1 an endless screw(5) and its tunnel or envelope (4).

Still in the classical way, the excavated materials mixed into thewatery fluid are conducted through the head (2) by conduits notrepresented, and are brought together in the inside chamber (3) whencethey are extracted (6) toward the rear (4, 5). Naturally, a part ofthese excavated materials will circulate more or less easily around thehead (space 12) and still less easily around the fixed skirt (8) of theboring machine in the interspace (13).

The specialist in the field knows that the problems of wear and ofblockage or jamming are the following:

Wear on the cutting tools situated on the front face (7).

Wear on the overcut tools (24).

Wear on the skirt (8) and even where applicable occurrences of jammingby the blocks (14) which could not be sufficiently disintegrated.

Wear on the front and side faces.

Wear and, where applicable, blockage or jamming at the level of theextraction system, especially when the latter consists of a screw andits envelope (4, 5).

Within prior art, heavy slurries are used comprising water, clay and/orpolymers. These materials give suitable results but it would appear verydesirable to improve them in order to lengthen the time betweenmaintenance operations which would be of considerable advantage.

Moreover, the use of heavy slurries of prior art requires extremelycumbersome preparation stations (which becomes prohibitive in a cityenvironment, for example) and costly. The slurry requires enormousamounts of water, which creates problems of an ecological nature, and isa liquid material, which poses a serious problem regarding protection ofthe environment at the level of discharges. Finally, these slurriesloaded with excavated material are difficult to remove from theextraction systems, for example a rolling conveyer, with thedifficulties aggravated by any slope.

The purpose of the invention is to propose a technique which greatlyreduces the wear on the parts and this greatly increases the timebetween maintenance operations, and makes it possible to eliminate theconstraints on using heavy slurries.

According to the invention, any clay is used capable under theconditions described here, of forming a coating of debris and of theendangered parts, and to adhere to it without the ill-fated “sluicing”phenomenon.

A large number of clays exist and the specialist in the field will knowhow to use the most interesting ones by doing simple tests like the onewhich will be described below, all readily performed. A clay ispreferably selected whose source is as close to the work site aspossible, for the obvious reasons of transporting expense.

The foam will be formed with the aid of a known foaming agent or theirmixtures.

One will preferably choose, for the convenience of the mixingoperations, a liquid foaming agent or surfactant (or a liquid mixture).

A representative compound of the invention is comprised of 34 liters offoam precursor watery liquid to 66 liters of clay.

For the same pumped volume of 100 liters, the classical prior art uses90 liters of water to 10 liters of bentonite.

APPLICATION EXAMPLE Test Procedure

The test cell is represented in FIG. 4. This simple cell will enable thespecialist in the field to select quickly by routine laboratory teststhe clay(s) and the surfactant(s) (and classical additives) to use, aswell as the proportions of gas such as compressed air, to adapt thepresent description to each particular case; it will be understood thatit is impossible to present here an example of the innumerablecombinations of formations to excavate and type of boring machine,cutting tools and cutting tool placement. On the other hand, theteaching of the invention will be applicable, generally, due to thepresent example, with only the adaptations within the purview of thespecialist in the field, to make a foam suitable to remain sufficientlystable and able to transport the excavated material.

The cell includes a receptacle 40 in which a steel wear plate (41)immersed in the material to be tested (42) is turned.

This test procedure, for example at 100 rpm in a receptacle of 10liters, is particularly representative of the wear of the extractionscrew which represents the most serious problem.

At the head of the tunnel boring machine a clay foam formed of:

clay: 66 liters.

foaming watery mixture (water and additives): 34 liters. is prepared.

Among the additives, the foaming agent is a mixture of appropriate,commercially available surface active agents yielding a stable foam ofgood quality with good suspension properties.

The test performed (as described above in relation to FIG. 4) wouldconsist of comparing the wear on the metal surfaces engendered bygneiss. The results are the following:

on gneiss without additive: wear level: 100.

on gneiss+water: wear level: 20

on gneiss+water+bentonite+clay: wear level: 29

on gneiss+above clay foam mixture: wear level: 1 to 2.

These tests were confirmed on a sample of clay foam after passagethrough the cutting head of a tunnel boring machine.

The foam is injected into the tunnel boring machine in the classicalway, by known turning joints, which thus does not require modificationof the machine.

The foam according to the invention may be injected by the front faceonly, but preferably double injection into the front face and into theback face to facilitate extraction will be carried out.

The test reveals an extraordinarily low wear level which differs by anorder of magnitude.

Without wishing to be limited by any theory, the applicant favors thehypothesis that coating by foam of abrasive particles, cutting tools andsurfaces of the machine and of the formation occurs with the formationof interfaces of good adhesion (which are not destroyed or reformed) andin such a way that, to an unexpected degree, reduction of the particularfriction coefficients takes place.

The invention likewise presents great interest in the use of the “thrusttube.” These systems, schematically represented in FIG. 3, are tubes orrings of concrete or analogous material (30) joined to the back of thetunnel boring machine (9) and thrust toward the front by jacks (32).Their function is dual: transmission of the thrust and displacement tothe tunnel boring machine, and consolidation or shoring-up of thetunnel. Their peripheral surface is thus essentially in contact with thetunnel wall (31).

It has been noted that for the reasons indicated above sliding wasgreatly facilitated by the injection of the clay foam according to theinvention.

What is claimed is:
 1. A method of boring a tunnel with a tunnel boringmachine comprising injecting just before the cutting tools of therotating head of the boring machine and the formation to be bored, anaqueous foam containing at least one clay, at least one surfactant andat least one gas in proportion to produce a good quality, stable foamwith the formation material and discharging the material from the tunnelvia the discharge of the boring machine.
 2. The method of claim 1wherein an already formed foam is injected from the internal dischargechamber of the boring machine.
 3. The method of claim 1 wherein the gasis air.
 4. The method of claim 1 wherein the gas is compressed air orcompressed nitrogen.
 5. The method of claim 1 wherein the foam isinjected at the lateral surfaces of the thrust tubes of the boringmachine.